Respiratory Failure
Any condition in which the respiratory
system fails to do its primary function:
Oxygenate arterial blood
and eliminate CO2
Function of Respiratory
System
Oxygenate arterial blood and
eliminate CO2
Usually a combination of the clinical features of the
underlying disease plus signs & symptoms of
hypoxemia & hypercapnia!
•  Dyspnea
•  Respiratory rate
•  Alveolar ventilation
–  Adequate measure cannot be made at
bedside
–  Nothing can be assumed about alveolar
ventilation by looking at RR & VT
•  Use of accessory muscles &/or
retractions
•  Cyanosis
•  Dyspnea
•  Increased RR
•  Use of accessory
muscles
•  Cyanosis (?)
•  ! in mental status
•  Weakness
•  Muscle tremor or
twitching
•  Drowsiness,
lethargy
•  Somnolence
•  Irritability
•  Coma
•  Agitation,
restlessness
•  Increased ICP
•  Cardiac arrhythmias
•  Tachycardia
•  Increased BP
•  Peripheral
vasoconstriction
–  Hard to draw ABG
–  Hard to do PO
–  Pallor
•  Diaphoresis
•  Spontaneous inspiration
–  Diaphragm contracts
–  Intercostal muscles pull outward to enlarge
thorax
–  Intrapleural pressure drops
(-4 to -10 cmH2O)
–  Air rushes in until alveolar pressure =
atmospheric pressure
•  Expiration
•  WOB = amount of effort required to
overcome compliance and resistance of
lungs and thorax
Evaluation of ventilatory mechanics
provides information about the
ease with which the lungs may be
inflated and the effectiveness of the
respiratory muscles
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Compliance
Airway resistance
Respiratory rate
Lung volumes
Airway pressures
•  Lung normally very compliant
•  Compliance = ! volume/ ! pressure
•  If lung, thorax is more difficult to distend
= decreased compliance " leads to
increased WOB
•  Causes of decreased compliance:
–  Fibrotic lungs (Pulmonary Fibrosis)
•  Secretions, fluid
•  Restriction of chest wall motion
•  RAW is the relationship between
•  Airway resistance = ! pressure/flow
•  Increased RAW " # WOB
•  Causes of increased RAW
•  Reliable indicators of patient’s ability to:
–  Maintain spontaneous ventilation
–  Reverse atelectasis
–  Mobilize secretions with effective cough
•  Measurement is
–  Quick
–  Easy
–  Low cost
•  Respiratory rate
–  Normal = 12 - 20 BPM
–  Most accurate to measure x 1 minute
–  If RR $ " need to # VT to maintain
adequate minute ventilation
–  If RR # " # VD
–  >35 = impending RF
•  Lung volumes - Minute Ventilation
–  Total volume of air exhaled in 1 minute
–  Normal = 5 - 7 LPM
–  If adequate - PaCO2 will remain normal
–  # will normally cause PaCO2 to $
–  Indirect evaluation of mechanical ability to
maintain ventilation
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Pain, anxiety
Fever
Hypoxemia
Hypercarbia
Acidosis
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# shunt
# VD
Early stage of RF
Diet high in
carbohydrates
•  Lung volumes - Tidal Volume
–  Volume of air inspired or expired passively
in a respiratory cycle
–  Normal = 5 - 7 ml/kg
–  Most accurate to measure exhaled minute
volume, then divide by RR
.!
VT = VE ÷ RR
•  Lung volumes - Vital Capacity
–  Maximum volume exhaled after a maximal
inspiration
–  Normal = 65 - 75 ml/kg
–  <15 ml/kg = impending RF
–  SVC measured with spirometer
–  Requires patient cooperation
•  Lung volumes - Vital Capacity
–  Best determinant of ventilatory reserves i.e.
respiratory muscle strength & volume
capacity for:
•  adequate cough
•  secretion clearance
•  prevent & reverse atelectasis
•  Lung volumes - Why monitor?
–  Changes in lung volumes have a direct
effect on gas exchange at the alveolarcapillary level
–  Reflects:
•  Mechanical function of pulmonary system
•  Changes in disease process
•  Responsiveness to therapy
•  Lung volumes - Who is monitored?
–  Intubated patients
•  Being considered for MVS
•  Receiving MVS
•  Being weaned from MVS
•  With abnormal respiratory patterns
•  Lung volumes - Who is monitored?
–  Non-intubated patients
•  Pre-op evaluation
•  With RR > 30
•  With neuromuscular disease
•  With CNS depression
•  With deteriorating ABGs
•  NIP, NIF
–  Normal = > -80 cmH2O
–  < -25 cmH2O = need for MVS
–  Reflects muscular strength for cough &
prevention of atelectasis
–  Patient instructed to inhale through
occluded airway attached to NIP gauge
–  Record negative pressure generated
•  PEP
–  Normal > +100 cmH2O
–  < +40 cmH2O = need for MVS
–  Reflects muscular strength for cough &
prevention of atelectasis
–  Patient instructed to blow through occluded
airway attached to pressure gauge
–  Record positive pressure generated
•  PEFR, MEFR
–  Normal = > 350 LPM
–  Maximum flow generated during FVC
–  Use peak flow meter
–  Assesses:
•  Degree of airway obstruction present
•  Response to bronchodilator therapy
•  Ability to generate high flow rates for coughing
Spirometers
•  Bellows
–  Water-sealed spirometer (Collins)
–  Exhaled volume spirometer (Puritan
Bennett)
–  Volume collectors
•  Turbine-driven
–  Wrights, Draeger, Fraser Harlake
–  Use miniature vanes or rotors that revolve
when exposed to gas flow which then
moves a needle on the gauge to record
volume
•  Flow transducers
–  Calculate volume by flow/time
–  Small, lightweight
–  2 types
•  Flow transducer
–  Pressure differential
•  Measure pressure difference across a
membranes
•  Fleisch pneumotach, V-O pneumotach
•  Flow transducer
–  Vortex-shedding
•  Vortex created by struts
•  Ultrasonic beam altered by vortex
•  Converts changes in turbulence to volume
•  Thermal units
–  Heated wire is cooled by gas flow which
changes electrical resistance of the wire
–  Converted to volume